1. Field of the Invention
The present invention relates to an optical fabricating method and apparatus, and particularly to an optical fabricating method and apparatus in which light is applied to a photo-curing material, which is cured by being irradiated with light, to allow fabrication of a structure.
2. Description of the Related Art
An optical fabricating method (laser lithography) has been conventionally known, in which photo-curing resin (photoresist), which has the property in that a portion thereof irradiated with light is cured, is used and a position irradiated with light is moved in accordance with a predetermined pattern to thereby form a three-dimensional structure (see Japanese Patent Application Laid-Open (JP-A) No. 56-144478). The photo-curing resin is cured in such a manner that a monomer in the resin is polymerized by absorption of light. The polymerized portion is solidified, and therefore, a non-cured liquid portion is removed to allow formation of a three-dimensional structure. In this optical fabricating method, the photo-curing resin exhibits a high absorptivity in an ultraviolet wavelength (typically, 300 nm to 400 nm), and an ultraviolet laser or an ultraviolet lamp is used as a light source.
However, in a conventional optical fabricating method utilizing ultraviolet irradiation (hereinafter referred to as an ultraviolet-irradiation optical fabricating method), there has been known that high speed fabricating is permitted, but processing accuracy is low. That is, in the ultraviolet-irradiation optical fabricating method, light is absorbed not only at a light focused point but also in portions irradiated with light and a curing reaction occurs therein. Therefore, processing accuracy is low (10 to several tens of μm), and a laminated structure merely can be formed.
In order to realize highly accurate fabricating, a fabricating method has been recently proposed, in which light having a wavelength which is double an absorption wavelength, that is, typically, 600 to 800 nm, is used instead of using ultraviolet irradiation, and the light is absorbed by a two-photon absorption phenomenon to allow formation of a three-dimensional structure (hereinafter referred to as a two-photon absorption optical fabricating method) (see Japanese Patent Application Publication (JP-B) No. 63-40650).
The two-photon absorption phenomenon has a nonlinear absorption characteristic in which an amount of absorption is proportional to a square of light intensity, and also has a high three-dimensional spatial resolution. With this characteristic employed, formation of a much finer structure can be realized compared with normal optical fabrication. Typically, the two-photon absorption optical fabricating method is used to form a three-dimensional structure. That is, the structure is decomposed into a set of dots and is cured with an irradiation position displaced by one point at a time, or a light focused spot is moved with light applied thereto, and an obtained set of lines is used to form the structure.
However, in either case of point curing and line curing, it is necessary that fixed light energy or more be absorbed so as to cure a unit area. Particularly, the two-photon absorption phenomenon has a low absorption probability compared with absorption in the ultraviolet-irradiation optical fabricating method. Although reduction of time is allowed with the output of a light source increased, ablation may occur at a fixed output or more, thereby resulting in breakage of resin.
As a result, in order to form structures of large size in great quantities, the two-photon absorption optical fabricating method using a two-photon absorption phenomenon has a small throughput, which practically becomes a problem. Therefore, reduction of the fabricating time is demanded.